Hypernatremia

General
- MCly due to lack of water access or excess insensible losses
  - Hypervolemic Hypernatremia
    - Iatrogenic
    - Exogenous Glucocorticoids/Cushings
    - Primary Hyperaldosteronism
  - Euvolemic Hypernatremia
    - Diabetes Insipidus
      - Nephrogenic vs. Central
  - Hypovolemic Hypernatremia
    - Renal Losses
      - Diuresis
      - Renal failure
    - Extrarenal losses
      - Typically diarrhea
Symptoms
- Progressive as hypernatremia worsens:
  - Restlessness or muscle weakness
  - Insominia
  - Lethargy
  - AMS
  - Coma
Management
- 1) Calculate free-water deficit (MdCalc): ((Na-140)/140) x TBW - Estimate TBW: 50% of body weight in women, 60% men
- 2) Administer deficit over 48-72h, without decrease in plasma Na+ concentration by >10mM/24h - A fast rate of correction (>10-12 mEq/day) has not been shown to be associated with worse outcomes 30948456
- 3) Account for Ongoing Water Losses
  - Calculate free-water clearance (FWC):
    - FWC = V x (1 – (UNa + Uk)/PNa) where V is urinary volume, UNa is urinary Na+, Uk is urinary K+, and PNa is plasma Na+
- 4) Insensible Losses ~10 ml/kg per day; less if ventilated, more if febrile
- 5) Add above components and correct the water deficit over 48-72h replace daily water loss
Treatment
- Oral water if tolerating PO intake
- If not tolerating oral intake:
  - Free water flushes via NG tube (400-600ml boluses q4-6hrs)
  - IV Dextrose in water (D2.5W or D5W)
  - If Hypovolemic:
    - 0.9% saline(isotonic) until euvolemic, then 5% dextrose (hypotonic) or 0.45% saline (hypotonic)
- DI: D5W is used
- Acidotic (diarrhea): Na+HCO3- is a 5% dextrose solution or may use LR
References
- 30948456 : Chauhan, K., Pattharanitima, P., Patel, N., Duffy, A., Saha, A., Chaudhary, K., Debnath, N., Van Vleck, T., Chan, L., Nadkarni, G. N., & Coca, S. G. (2019). Rate of Correction of Hypernatremia and Health Outcomes in Critically Ill Patients. Clinical journal of the American Society of Nephrology : CJASN, 14(5), 656–663. https://doi.org/10.2215/CJN.10640918